1. Field of the Inventive Concepts
The concepts disclosed herein are generally related to surgical devices, and more particularly, but not by way of limitation, to a surgical cutting tool and methods of using same.
2. Brief Description of Related Art
The human spine is a highly complex bone and connective tissue structure which includes over twenty vertebral bones coupled to one another so as to house and protect critical elements of the nervous system. In addition, the spine is a highly flexible structure, capable of a high degree of curvature and twist in multiple directions. The vertebral bones and connective tissue of a human spine are coupled sequentially to one another by a tri-joint complex which consists of an anterior disc joint and the two posterior facet joints. The anterior discs of adjacent vertebral bones are separated and cushioned by cartilage spacers referred to as intervertebral discs. The vertebral bones of the spine are classified as cervical, thoracic, lumbar, and sacral.
The cervical portion of the spine, which comprises the upper portion of the spine up to the base of the skull, is the most flexible of all the regions of the spine, and includes the first seven vertebrae. The twelve intermediate bones comprise the thoracic vertebrae, and connect to the lower spine which comprises the five lumbar vertebrae. The base of the spine is the sacral bones (including the coccyx).
A typical human vertebral bone consists of two essential parts: an anterior (front) segment, which is the vertebral body; and a posterior part—the vertebral (neural) arch—which encloses the vertebral foramen. The vertebral arch is formed by a pair of pedicles and a pair of laminae, and supports seven processes—four articular, two transverse, and one spinous.
The healthy adult human spine is generally S-shaped, having a lordotic curvature in the lumbar region and a kyphotic curvature in the thoracic portion and cervical portion. The lordotic curvature and the kyphotic curvature typically balance out in a healthy human spine, such that the healthy human spine has an overall vertical shape and overall approximately neutral curvature.
However, some disease processes or injuries may cause and excessive lumbar curvature known as lordosis, or an excessive thoracic curvature know as kyphosis in some patients. In some cases of spinal degenerative disease, developmental problems, or trauma, the alignment of the spine may become severely compromised, which may result in excess kyphosis, in some severe cease rendering the patient unable to carry on the normal activities of daily life, and subjecting them to significant pain and limited mobility.
Fortunately, several surgical procedures have been developed, to decrease the kyphotic curvature, increase the lordotic curvature, or combinations thereof, to return the spine closer to its healthy natural alignment.
One such surgical procedure, commonly known as a pedicle subtraction osteotomy (PSO), has been developed to correct the alignment of the spinal column such that the height of the spine is not significantly compromised, and such that the spine is realigned to approximate the natural curvature of the spine.
PSO is generally performed via a posterior access (e.g., through the back) to the spine, and involves removing all posterior features of one or more vertebrae, including the pedicles. Next, cancellous bone is removed from the vertebral body via two openings located at the former pedicle bases positioned on both sides of the spinal cord from the vertebral body such that a generally V-shaped longitudinal notch (relative to the spine) is formed in the vertebral body. Due to the proximate location of the spinal cord and adjacent nerve roots, a “bone bridge” (a posterior portion of the vertebral body which cannot be removed due to its location under the spinal cord) remains under the spinal cord and extends between the two openings. A portion of a ligament known as the posterior longitudinal ligament (PLL) may also extend over the bone bridge, between the bone bridge and the spinal column, in some cases.
To remove this bone bridge or the associated portion of the PLL, one or more surgical cutting tools are used, such as elevators to lift and move away the spinal cord and adjacent nerve roots, and one or more curettes, which may be manually pushed in or tapped with a surgical hammer to gradually cut, or chip, through the bone bridge or the PLL. Next, other suitable surgical cutting tools may be used to extract any cut-away portions of the bone bridge or PLL, while moving the spinal cord and adjacent nerve roots out of the way with an elevator.
After the bone bridge and PLL are cut away and extracted or removed from the vertebral body, the lateral wall portions of the vertebral body are similarly cut away so that the V-shaped notched formed in the vertebral body may be collapsed onto itself to re-shape the vertebral body into a wedge shape. The changed shape of the vertebral body may result in a change of the angle of the spine by increasing its lordotic curvature. The PSO procedure may be carried out on one or more vertebral bodies, as indicated in a particular case.
Supplemental support mechanisms, such as spinal support rods or plates, and appropriate fixation points along the spine, may then be used to secure the spine in any desired position and curvature such that a compressive force is maintained on the cut vertebral body or bodies, to facilitate the healing of the cut vertebral body, such that the cut may heal.
The removal of the bone bridge and the PLL from the posterior end of the vertebral body is a part of the PSO procedure that is prone to error and is highly dependent on surgeon skill and local patient anatomy. For example, curettes or other surgical cutting tools that may be used to cut the bone bridge and the PLL behave differently when encountering bone tissue versus encountering the PLL. Impinging or pushing against bone tissue with a curette produces little or no rebound of the curette, and impinging or pushing against the PLL with a curette may result in rebound of the curette, which may cause the curette to slip or move off-target. Further, the elevator or other surgical cutting tool used to lift the spinal column and adjacent nerve roots to move them out of the way may cause unintentional injury to such tissues. Additionally, the tight spaces and the proximity of the spinal cord and the adjacent nerve roots may result in neurological injuries or damage in some cases, where the curette, elevator, or other surgical cutting tool slip or otherwise become dislodged or displaced during the removal of the bone bridge and encounters the spinal cord or an adjacent nerve root.
Further, the force applied by the curette may cause the bone bridge to break up into one or more bone fragments which may have sharp edges and which may move or deflect in various directions after breaking off from the vertebrae. Deflection or movement of such sharp bone fragments is typically carefully controlled during the procedure, and the fragments are accounted for and carefully extracted from the surgical site, to avoid injuring adjacent nervous tissues and potential post-operative complications. However, the unpredictable deflection of bone fragments, as well as the number and size of fragments can vary significantly during each procedure, and the control and removal of such fragments are highly dependent on surgeon skill and patient anatomy, and add undesired complexity and time to the procedure.
Besides a PSO, other surgical procedures may be performed that involve cutting of bone or other tissue in locations where injuries to adjacent tissues are of concern, or where careful control of the resulting bone or other tissue fragments is desired.